In a physical machine (hereinafter also referred to as a “computer”), an operating state of the computer may be acquired to provide a backup, in order to enable execution of a process to continue even when a fault is generated within the computer during the execution of the process. The backup of the operation state of the computer may be acquired as a so-called “snapshot”. For example, even when the fault is generated within a working system computer, the snapshot of the operating state of the working system computer, acquired as the backup before the fault is generated, may be used to restore the operating state of the working system, computer before the fault is generated within a duplicating (or backup or copying) system computer.
On the other hand, in a VM (Virtual Machine), there are various proposed methods to acquire an operating state of the VM as the snapshot in order to cope with a situation in which the fault is generated within the VM. The operating state of the VM includes an operating state of a virtual processor (for example, a virtual CPU (Central Processing Unit)) and memory contents, where the virtual processor may run on (or operate in) a processor (for example, a CPU) of the computer in which the VM operates. In addition, the fault may include a fault that is caused by software and is generated within the VM, and a fault that is caused by hardware and is generated within the computer in which the VM operates.
According to the proposed method that provides the backup by acquiring the operating state of the VM as the snapshot, the operating state of the VM (operating state of the virtual CPU and memory contents) may be stored directly in a storage unit, such as a disk drive and the like, as backup data (that is, snapshot), in order to provide the backup. For this reason, it may take a relatively long time to perform a backup process, depending on a memory size allocated to the VM. Hence, a stop time of a working process may become relatively long when the working system VM is temporarily stopped during the backup process. On the other hand, when the working system VM is not temporarily stopped during the backup process, a data consistency cannot be maintained between the data of the VM restored using the backup data and the data of the working system VM. Furthermore, according to the proposed method, the VM may be restored using the backup data only when the fault is generated within the working system VM, and a reference to the backup data maintaining the data consistency cannot be made while the working system VM is operating. When the data consistency is not maintained, a state in which there is no dropout or discrepancy in a structure or meaning of the data when viewed front an application (or application program) that is executed in the working system VM (hereinafter referred to as an “application consistency”) cannot be maintained.
In the case of a method that stops the working system VM during the backup process in order to maintain the application consistency, the working process or service may be discontinued. In this case, when the working system VM is used in a data center and the like, a notification may be required to notify users that the working process or service is discontinued. On the other hand, in the case of a method that embeds an associating mechanism with respect to the storage unit for each application and writes contents of a buffer and cache into the storage unit when creating the snapshot, the method cannot be applied to an application that does not have the associating mechanism. In addition, in the case of a method that calls a snapshot creating application in the storage unit side from the working system side applied with the working system VM, functions need to be added with respect, to the working system and users need to be educated. In this case, when the working VM is used in the data center and the like, the storage unit side may require multiplicity management, scheduling, and security measures.
The applicant is aware of Japanese Laid-Open Patent Publications No. 2009-533777, No. 2009-80692, and No. 2007-183701, for example.
According to the prior art backup method, it may be difficult to appropriately provide a backup of the data of the VM while the working system VM is operating.